Method of producing cd(hg(scn)4)single crystals

ABSTRACT

Large Cd (Hg (SCN)4) single crystals are produced by crystallizing Cd (Hg (SCN)4) from a super-saturated solution thereof in solvent comprising a mixture of water and alcohol (for example, ethanol). Super-saturation of the crystallizing component in the solvent is achieved by changing the mixture ratio of the solvent components and/or by changing the temperature of the saturated solution of crystallizing component and solvent.

United States Patent [191 Grabmaier et al.

54} METHOD OF FliGDUCING 'canrg scrim SINGLE CRYSTALS [75] Inventors: Josef Grabmaier, Unterhaching;

Rolf Pliittner, Ottobrunn, both of Germany [73] Assignee: Siemens Aktiengesellschaft, Berlin and Munich, Germany [22] Filed: Feb. 28, 1972 [21] Appl. No.: 229,740

[30] Foreign Application Priority Data Mar. 4, 1971 Germany 2110425 [52] US. Cl 23/300, 23/305, 423/366 [51] Int. Cl B01j 17/00 [58] Field of Search 23/293, 300, 305; 423/99, I

[5 6] References Cited UNITED STATES PATENTS 3,020,123 2/1962 Schaeffer 423/366 ca [Hg (so/0 1 SOLUBILITY 5] Oct. 8, 1974 3,671,200 6/1972 Armington 23/300 OTHER PUBLICATIONSv (filem ical K bsTracts 1935 357763 29. Chem. Abs. 1963, V59, 60l4C. Chem. Abs. 1970, V73, 102545F.

Primary Examiner-Norman Yudkoff Assis an firem zzli ni Bertlstein Attorney, A gent, or Firm Hill, crdgsjsfiniisdn I w 7 Van Santen, Steadman, Chiara & Simpson [57] ABSTRACT I 14 Claims, 2 Drawing Figures n 25 an ETHANOL SULUBILITY PATENTED UN 8 I974 3. 840 347 suwzum Fig.2

Cd [Hg (saw), 1

TEMPERATURE [E] '1 "iv'rfi'nob awesome "entire (seam SINGLE CRYSTALS BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to methods of producing large single crystals and more particularly the methods of producing large cadmium-mercury tetrathiocyanate single crystals.

2. Prior Art Cadmium-mercury tetrathiocyanate crystals are known to be useful for non-linear frequency conversion of laser light so as to provide a high degree of efficiency. Suggestions have been proposed for growing such Cd [Hg (SCN) crystals from a solution in a silicic acid gel. In such a process, single crystals are produced with a disphenoid (i.e., bisphenoid) crystal form having maximum edge lengths of 3 to mm. However, such crystal shapes or forms are not suited for use in frequency conversion of laser light and such disphenoid crystals must be shaped, as by grinding, to useful forms. The reformed crystals have an edge length of only 1 to 2 mm. Since the yield of a frequency conversion process increases with the square of the linear dimension of the crystal utilized, it is highly desirable to provide as large a crystal as possible.

Other conventional crystal growing processes are known, for example, growing large crystals from a molten mass of a given material. However, since Cd [Hg (SCN),] is decomposable at temperatures above 200 C., such a method is unsuitable. Similarly, growing of Cd [Hg (SCN),] crystals from an aqueous solution is unsuitable since a crystal of this compound has very low solubility in water, for example, a solubility of about 2' l0 moi/liter (9.3 grams/liter) in water at 60 C. However, to practically produce sufficiently large crystals, higher solubility is necessary, for example, a solubility up to about 100 grams/liter is required.

SUMMARY OF THE INVENTION The invention provides large cadmium-mercury tetrathiocyanate single crystals and relatively simple, straightforward methods of producing the same.

In accordance with the principles of the invention, a super-saturated solution of cadmium-mercury tetrathiocyanate (Cd [Hg (SCN) is produced in a solvent comprising a mixture of water and alcohol and the Cd [Hg (SCNM crystallizes therefrom as a large single crystal. A preferred alcohol is ethanol and a preferred solvent comprises a 77 percent ethanol concentration in water. Such a preferred solvent is saturated with Cd [Hg (SCN)4] and the ethanol concentration is lowered,

as by evaporation, down to about 25 percent or the ethanol concentration is raised up to about 95 percent to produce a super-saturated solution. yielding the desired large single crystals. In an alternativeembodiment, a Cd [Hg (SCNM saturated ethanol-water mixture is produced at about 50 C. and the temperature of the mixture lowered to about C. to produce a supersaturated solution, yielding the desired large single crystals.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graphic illustration showing the relation between Cd [Hg (SCN) solubility and ethanol concentrations; and

2 FIG. 2 is a graphic illustration showing the relation between Cd [Hg (SCNM-solubility and temperature.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention generally comprises forming large single crystals of Cd [Hg (SCN)4] from a Cd [Hg (SCN),] supersaturated solution that includes a mixture of water and alcohol.

Ethanol is a preferred alcohol in the alcohol-water solvent system of the invention because of the high solubility of Cd [Hg (SCN) in an ethanol-water system, for example, the solubility of Cd [Hg (SCN).,] in an ethanol-water system having about a percent concentration of ethanol is about 73 grams/liter. Other low boiling alcohols may also be used, such as methanol, propanol, etc., or mixtures thereof.

In accordance with certain embodiments of the invention, a solvent system is produced having an ethanol concentration of at least about 75 percent and not more than about 77 percent in water and this solvent system is then provided with an amount of Cd [Hg (SCN) sufficient to no more than completely saturate with the solvent system (i.e., at least saturate the solvent system). However, the solvent system includes water-alcohol mixtures wherein the concentration of alcohol ranges from about 25 to about percent.

In a first embodiment, such a partially saturated or saturated Cd [Hg (SCN)i]-solvent solution is altered so that the concentration of for example ethanol is lowered, down to as low as about 25 percent so that a super-saturated solution is produced, and large single crystals of Cd [Hg (SCN),] crystallize therefrom.

In a second embodiment, such a partially saturated or saturated Cd [Hg SCN),]-solvent solution is altered so that the concentration of ethanol is increased, up to as high as about 95 percent sothat a super-saturated solution forms and relatively large single crystals of Cd [Hg (SCN) crystallize from such solution.

In a third embodiment, such a partially saturated or saturated Cd [Hg (SCNM-solvent solution is provided at an upper temperature of about 50 C. and then cooled down to a lower temperature of about 2 0 C. so

that a super-saturated solution forms and relatively large single crystals of Cd [Hg (SCN)' crystallize therefrom;

In the first embodiment, the super-saturation of a solution is achieved, for example, by removing the ethanol vapors that form above the solution, as by blowing such vapors away. This lowers the concentration of ethanol in the solvent and causes a decrease in the solubility of the crystallizing component in the solution so that crystallization of a desired large single crystal of Cd [Hg (SCNM takes place.

In the second embodiment, the super-saturation of the solution is achieved, for example, by subjecting the vapors above the solution with a water-absorbing substance, as a hydrophilic calcium or the like material so that the concentration of ethanol is increased in the solution. When the ethanol concentration is increased from its initial value of 77 percent up to about 95 percent, the solubility ofCd [Hg (SCN) is decreased so that the crystallization of a desired large single crystal of Cd [Hg (SCN) takes place.

Preferably, the crystallization of Cd [Hg (SCN) is effected at temperatures of about 20 C. It is particu- 3 larly advantageous to provide a super-saturated solution of the type described at about 50 C. and then cool it down to about 20 C. since the solubility of Cd [Hg (SCNM is lower at 20 C. than at 50 C. so that as large as possible single crystals are produced. However. temperatures above 50 C. cause a small amount of decomposition of Cd [Hg (SCN) over a period of some weeks (which is required for proper growth) and are thus to be avoided.

FIG. 1 illustrates the quantitative relation between the solubility ofCd [Hg (SCN) and the concentration of ethanol in water, at 204 C. As can be seen, the solubility of Cd [Hg (SCN) in'ethanol-water solutions having an ethanol concentration ranging from about 25 to about 75 C. increases drastically upwards from about 5g/l with increases in ethanol concentration and reaches a maximum in a solution having about a 77 percent ethanol concentration. The solubility of Cd [Hg (SCN) in solvent solutions having about 77 percent ethanol therein is about 73 grams/liter. However, with solvent solutions having ethanol concentrations ranging from about 77 to about 95 percent, the solubility of Cd [Hg (SCN) decreases substantially with increased concentrations of ethanol.

In accordance with the principles of the invention as illustrated at FIG. 1, at least about 5 g/l of Cd[Hg(SCN) are added to an alcohol-water solvent system and the concentration of one of the solvent components (alcohol or water) is changed so as to decrease the solubility of Cd[Hg(SCN) in the resulding system and cause large single crystals of Cd[Hg(SCN) to form. With initial alcohol-water solvent systems having an alcohol concentration in the range of about at least 25 percent and up to about 77 percent, the alcohol concentration is decreased below that in such initial solvent systems. On the other hand,

the initial alcohol-water solvent systems having an alcohol concentration in the range of about at least 77 percent and up'to about 95 percent, the alcohol concentration is increased above that in such initial solvent systems.

In order to grow large single crystals of Cd [Hg (SCN) from an ethanol-water solvent system having about 75 percent ethanol in water (and an amount of Cd [Hg (SCN) therein), the concentration of one of the solvent components, such as ethanol is altered, as by lowering it down to about 25 percent by removing ethanol vapors that are present above the solution. The solubility of the Cd [Hg- (SCN) is thereby decreased to about 5 grams/liter. In this manner, a controllable super-saturation of the crystallizing solution is readily attained and yields crystallization of the dissolved crystallizing components.

Similarly, a controllable super-saturation is obtained when the ethanol v concentration is increased from about 77 to about 95 percent (or the concentration of water is decreased correspondingly) as illustrated on the right hand side of the graph at FIG. 1, starting at the v maximum point of solubility. Increases in the ethanol concentration or decreases in the water concentration are readily achieved by treating the vapor above the solution with a water-removing substance or by removing water from the solution itself.

Super-saturation of the solution (Cd [Hg(SCN) ethanol-water mixture) is also achieved by slowly adding pure water or pure alcohol to the solution. In one form, an ethanol-water mixture with an, ethanol con- 4 centration less than 77 percent is provided by additions of pure water and in another form, an ethanol-water mixture with an ethanol concentration greater than 77 percent is provided by additions of pure ethanol. Formation of undesired foreign nuclei that might occur' with a decreasing liquid level, as by thedeposition thereof along the side walls of a container, are readily avoided with the above described embodiments since the liquid level remains constant or increases.

A means of achieving super-saturationother than by changing the ethanol-water mixture ratio is by lowering the solubility of Cd [Hg(SCN) in the ethanol-water mixture through a decrease in the solution temperature. The relation between the solubility of Cd [Hg (SCN) and temperature is illustrated at FIG. 2. in accordance with theprinciples of the invention as illustrated at FIG. 2, at least about 5 g/l of Cd[Hg(SCN) are added to an alcohol-water system which is maintained at about 50 C. so as to form a solution of the tetrathiocyanate in the solvent system and then the resulting solution is cooled to a temperature of about 20 C. so as to decrease the solubility of Cd[Hg(SCN) in the solution and cause large single crystals of Cd[Hg(SCN) to form. Preferably, the saturated or partially saturated solution is produced at a temperature of about 50 C. and then cooled to about 20 C. for crystallization therefrom of a desired relatively large single crystal. A minor disadvantage of this embodiment is that Cd [Hg (SCN) in a solution with a temperature over 50 C. tends to slightly decompose and in a few days under such conditions, the solution becomes a pale yellow and gives rise to the possibility-of contamination in crystals obtained therefrom. j

Accordingly, the invention broadly provides a method of producing cadmium-mercurytetrathiocyanate single crystals by forming a saturated or a supersaturated solution of cadmium-mercury tetrathiocyanate in a solvent comprising a mixture of alcohol and water and crystallizing the cadmium-mercury tetrathiocyanate therefrom as a relatively large single crystal.

As is apparent from the foregoing specification, the present invention is susceptible of being embodied with various alterations and modifications and may differ particularly from those that have been described in the preceding specification and description. For this rea son, it is to be fully understood that all of the foregoing is intended to be merely illustrative and is not to be construed or interpreted as being restrictive or otherwise limiting of the present invention, excepting as is set forth and defined in the hereto-appended claims.

We claim as our invention:

1. A method of producing cadmium-mercury tetrathiocyanate single crystals comprising:

adding at least about 5 grams of Cd[Hg(SCN) per liter of an initial solvent system comprised of a mixtureof solvent components consisting essentially of about 25 to about percent of a low boiling alcohol and water so as to achieve a solution of said Cd[Hg(SCN).,] in said solvent system; and

changing the concentration of one of said solvent components in said solution up to saturation to attain a resultant solution so that when the alcohol concentration in said initial solvent system is in the range of at least 25 percent and up to 77 percent, said resultant solution has an alcohol concentration lower than that of said initial solvent system and when the alcohol concentration in said initial solvent system is in the range of about at least 77 percent and up to 95 percent, said resultant solution has an alcohol concentration greater than that of said initial solvent system whereby cadmiummercury tetrathiocyanate is crystallized from said resulting solvent system as a relatively large single crystal. I 2. A method as defined in claim 1 wherein said solvent system comprises a mixture of ethanol and water.

3. A method as defined in claim 2 wherein changing the concentration of one of said solvent components comprises removing an amount of a solvent component until said resultant solution is obtained.

4. A method as defined in claim 3 wherein said solution is changed by removal of an amount of ethanol sufficient to achieve said resultant solution.

5. A method as defined in claim 4 wherein removal of ethanol from said solution is achieved by removal of ethanol vapors above said solution.

6. A method as defined in claim 3 wherein said solution is changed by removal of an amount of water sufficient to achieve said resultant solution.

7. A method as defined in claim 6 wherein removal of water from said solution is achieved by'removal of water vapor above said solution.

8. A method as defined in claim 7 wherein the water vapors are removed by contacting said vapors with a water-absorbing substance.

9. A method as defined in claim 2 wherein changing the concentration of one of said solvent components comprises adding an amount of a solvent component until said resultant solution is obtained.

10. A method as defined in claim 9 wherein said solution is changed by adding an amount of ethanol sufficient to achieve said resultant solution.

11. A method as defined in claim 10 wherein said solution is changed by adding an amount of water sufficient to achieve said resultant solution.

12. A method as defined in claim '1 wherein changing the concentration of one of said solvent components is achieved while said solution is at a temperature of about 20 C. g

13. A method as defined in claim 1 wherein said solvent system is maintained at about 50C. during the addition of the Cd[Hg(SCN) and during changing of the concentration of one of said solvent components in said solution, said solution is cooled down to about 20 C.

14. A method of producing cadmium-mercury tetrathiocyanate single crystals comprising:. 7

adding at least about 5 grams of Cd[Hg(SCN) per liter of an initial solvent system comprised of a mixture of solvent components consisting essentially of about 25 to about percent of ethanol and water so as to achieve a solution of said chemical formula in said solvent system; and

changing the concentration of one of said solvent components in said solution up-to saturation to attain a resultant solution so that when the-ethanol concentration in said initial solvent system is in the range of at least 25 percent and upto 77 percent, said resultant solution has an ethanol concentration lower than that of said initial solvent system and when the ethanol concentration in said initial solvent system is in the range of about at least 77 percent and up to 95 percent, said resultant solution has an ethanol concentration greater than that .of said initial solvent system whereby cadmiummercury tetrathiocyanate is crystallized from said resulting solvent system as a relatively large single crystal. 

1. A METHOD OF PRODUCING CADIMUM-MERCURY TETRATHIOCYANATE SINGLE CRYSTALS COMPRISING: ADDING AT LEAST ABOUT 5 GRAMS OF CD(HG(SCN)4) PER LITER OF AN INITIAL SOLVENT SYSTEM COMPRISES OF A MIXTURE OF SOLVENT COMPONENTS CONSISTING ESSENTIALLY OF ABOUT 25 TO ABOUT 95 PERCENT OF A LOW BOILING ALCOHOL AND WATER SO AS TO ACHIEVE A SOLUTION OF SAID CD(HG(SCN)4) IN SAID SOLVENT SYSTEM; AND CHANGING THE CONCENTRATION OF ONE OF SAID SOLVENT COMPONENTS IN SAID SOLUTION UP TO SATURATION TO ATTAIN A RESULTANT SOLUTION SO THAT WHEN THE ALCOHOL CONCENTRATION IN SAID INITIAL SOLVENT SYSTEM IS IN THE RANGE OF AT LEAST 25 PERCENT AND UP TO 77 PERCENT, SAID RESULTANT SOLUTION HAS AN ALCOHOL CONCENTRATION LOWER THAN THAT OF SAID INITIAL SOLVENT SYSTEM AND WHEN THE ALCOHOL CONCENTRATION IN SAID INITIAL SOLVENT SYSTEM IS IN THE RANGE OF ABOUT AT LEAST 77 PERCENT AND UP TO 95 PERCENT, SAID RESULTANT SOLUTION HAS AN ALCOHOL CONCENTRATION GREATER THAN THAT OF SAID INITIAL SOLVENT SYSTEM WHEREBY CADIUM-MERCURY TETRATHIOCYANATE IS CRYSTALLIZED FROM SAID RESULTING SOLVENT SYSTEM AS A RELATIVELY LARGE SINGLE CRYSTAL.
 2. A method as defined in claim 1 wherein said solvent system comprises a mixture of ethanol and water.
 3. A method as defined in claim 2 wherein changing the concentration of one of said solvent components comprises removing an amount of a solvent component until said resultant solution is obtained.
 4. A method as defined in claim 3 wherein said solution is changed by removal of an amount of ethanol sufficient to achieve said resultant solution.
 5. A method as defined in claim 4 wherein removal of ethanol from said solution is achieved by removal of ethanol vapors above said solution.
 6. A method as defined in claim 3 wherein said solution is changed by removal of an amount of water sufficient to achieve said resultant solution.
 7. A method as defined in claim 6 wherein removal of water from said solution is achieved by removal of water vapor above said solution.
 8. A method as defined in claim 7 wherein the water vapors are removed by contacting said vapors with a water-absorbing substance.
 9. A method as defined in claim 2 wherein changing the concentration of one of said solvent components comprises adding an amount of a solvent component until said resultant solution is obtained.
 10. A method as defined in claim 9 wherein said solution is changed by adding an amount of ethanol sufficient to achieve said resultant solution.
 11. A method as defined in claim 10 wherein said solution is changed by adding an amount of water sufficient to achieve said resultant solution.
 12. A method as defined in claim 1 wherein changing the concentration of one of said solvent components is achieved while said solution is at a temperature of about 20* C.
 13. A method as defined in claim 1 wherein said solvent system is maintained at about 50* C. during the addition of the Cd(Hg(SCN)4) and during changing of the concentration of one of said solvent components in said solution, said solution is cooled down to about 20* C.
 14. A method of producing cadmium-mercury tetrathiocyanate single crystals comprising: adding at least about 5 grams of Cd(Hg(SCN)4) per liter of an initial solvent system comprised of a mixture of solvent components consisting essentially of about 25 to about 95 percent of ethanol and water so as to achieve a solution of said chemical formula in said solvent system; and changing the concentration of one of said solvent components in said solution up to saturation to attain a resultant solution so that when the ethanol concentration in said initial solvent system is in the range of at least 25 percent and up to 77 percent, said resultant solution has an ethanol concentration lower than that of said initial solvent system and when the ethanol concentration in said initial solvent system is in the range of about at least 77 percent and up to 95 percent, said resultant solution has an ethanol concentration greater than that of said initial solvent system whereby cadmium-mercury tetrathiocyanate is crystallized from said resulting solvent system as a relatively large single crystal. 